158 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 4, NO. 4. 
of the bee-larva, never leaving the latter, and rarely shifting its 
position. 
Of the three larvae of Leacospis afhnis only one was alive on 
July 16th, and this went through the first moulting process early 
in the morning of July 17th, being about three days old. This 
number of days is the time within which the larva has to rid itself 
of its rivals in the cell, and considering its great activity on the 
first and second days of its existence it undoubtedly gets through 
with its destructive work long before the time is up. Already on 
the third day it shows a tendency to become more sedentary, and it 
passes the last few hours before moulting in a rather quiet state. 
The secondary larva of my specimen showed a length of about 
2 mm. immediately after the moult had taken place, it had therefore 
within three days doubled its length by taking up the contents of 
the destroyed rival larva, as also by feeding to a very slight extent 
on the bee-larva. From now on it partook of the juices of the bee- 
larva without causing any visible injury to the latter, and in this 
manner kept it in a fresh condition throughout the procedure. 
For this purpose it is equipped with very sharp, small mandibles. 
(Fig. 6.) The bee-larva gradually assumed a shrivelled appear- 
ance, and on July 26th nothing was left of it except the entirely 
empty skin. 
On July 31st the Leucospis-larva pupated, and on August 14th 
a male imago appeared. The larva does not construct a cocoon, 
the pupa lies inside of the cell or of the Osmia-cocoon, if the bee- 
larva has had time to construct one. 
We have therefore for this specimen of Leacospis aflinis a 
duration of the different stages as follows : 
egg stage about 3 days, 
larval stage 17 days, 
pupal stage 14 days. 
Female specimens making their appearance at the same time 
of the year as this male specimen certainly produce another brood, 
the members of which pass the winter in the larval state and trans- 
form into the perfect insects around the beginning of July or some- 
what later. As stated at the beginning of this paper, a young 
larva and an egg of this parasite were found in two different nests 
of Osmia simillima as late as September 18th. From the evidence 
on hand it can be stated that there are two generations a year. The 
